1. Field of the Invention
The present invention relates to a measurement system and a method which measure a Specific Absorption Rate (SAR) at which electromagnetic energy from a radiating source, such as a mobile phone or the like, is absorbed in a dielectric medium during exposure.
2. Description of the Related Art
A Specific Absorption Rate (SAR) is a rate at which electromagnetic energy from a radiating source is absorbed in a dielectric medium and specifically defined as a value proportional to the second power of electric field strength (|E|2) as expressed by the numeric equation (1).
                    SAR        =                              σ            ⁢                                                          E                                            2                                ρ                                    (        1        )            where σ represents the electric conductivity (S/m) of a dielectric medium, and ρ is the density (kg/m3) of the medium. The unit of measurement of SAR is W/kg. The SAR is specifically used to evaluate electric energy absorbed in a human body when a mobile phone or the like is used near the human body (see non-patent document 1).
When measuring the SAR, the electromagnetic field generated in the dielectric medium is detected by an electric field probe using, for example, a small dipole antenna and a diode, and the measured electric field is converted into a SAR value in accordance with the equation (1).
FIG. 1 shows an example of a related art of SAR measurement system. This SAR measurement system includes tissue-equivalent liquid 101 (called “phantom”) having predetermined dielectric constants so as to simulate a human body, a phantom shell 102, an electric field detection probe 103, a probe scanning robot 104, a signal cable 105, an electric field detection apparatus 106, and a measurement control and data analysis processing apparatus 107. In this measurement system, a mobile phone 108 as a radiating source is supported by a supporting apparatus 109 and the electromagnetic field generated in the phantom by the mobile phone 108 is measured. Specifically, the electromagnetic field in the phantom is 3-dimensionally measured by the electromagnetic probe 103 scanned by the probe scanning robot 104, and thus a 3-dimentional SAR distribution is obtained.
However, since this method takes a long time in measuring the SAR, an SAR measurement method as follows has been proposed for the purpose of reducing measurement time. Namely, the electromagnetic field and thus SAR in the medium is measured only 2-dimensionally and the SAR distribution along the remaining direction (phantom depth direction) is empirically estimated, thereby realizing a faster measurement in this proposal. (see non-patent document 2). In addition, there has been proposed another method where the 2-dimensional SAR data and the SAR data in phantom depth obtained along only one line in the depth direction are used to estimate the 3-dimensional SAR distribution using an appropriate approximate expression (see non-patent document 3). Moreover, there has been yet another proposal where two different sets of 2-dimensional data of amplitude and phase of electric field or magnetic field are measured and the SAR distribution in phantom depth is calculated in accordance with the two sets of the 2-dimentional data so as to estimate the 3-dimensional SAR distribution (see patent-related document 1).                [Patent-related document 1] Japanese Patent Application Laid-Open Publication No. 2006-47297.        [Non-patent document 1] Thomas Schmid, Oliver Egger, and Niels Kuster, “Automated E-Field Scanning System for Dosimetric Assessment,” IEEE Trans. Microwave Theory and Tech., Vol. 44, No. 1, pp. 105-113, January 1996.        [Non-patent document 2] M. Y. Kanda, M. G. Douglas, E. D. Mendivil, M. Ballen, A. V. Gessner, and C. K. Chou, “Fast Determination of Mass-Averaged SAR from 2-D Area Scans,” IEEE Trans. Microwave Theory and Tech, Vol. 52, No. 8, pp. 2013-2020, August 2004.        [Non-patent document 3] O. Marckel, J. Ch. Bolomey, and G. Fleury, “Parametric model approach for rapid SAR measurements”, IMTC2004, Instrumentation and Meas. Tech. Conf., pp. 178-183, Como, Italy, May 2004.        